Safety stitch sewing machines



March 31, 1964 v J. SIGODA 3,126,850

SAFETY STITCH SEWING MACHINES Filed May 8, 1961 3 Sheets-Sheet 1 FIG. 1

l 9-, w 3 ql2 1 I K1- I0 09 N co 9 N INVENTOR.

VICTOR J. SIGODA March 31, 1964 v. J. SIGODA 3,126,850

SAFETY STITCH SEWING MACHINES Filed May 1961 3 Sheets-Sheet 2 'INVENTOR. VICTOR J. S/GODA United States Patent Ofiice Patented Mar. 31, 1964 York Fiied May 8, 1961, Ser. N 103,562 1 Claim. (Cl. 112-162) This invention relates to sewing machines of the safety stitch type which in a single operation sew a join or securing seam and simultaneously overcast the edges of the work plies. More particularly, it concerns a new mode of operation for such machines in which the two different types of stitching are formed at different rates. This mode of operation is useful whether the join seam is of the lockstitch type disclosed in Sigoda Patent No. 2,973,- 731 or of the two thread chainstitch type disclosed in Sigoda application Serial No. 30,682, filed May 20, 1960.

In all previously known safety stitch machines, since the feed stroke, which determines the stitch length, is the same for both types of stitching, and both sets of stitchforming elements are operated at the same rate, the formation of both types of stitching proceeds at the same pace. The more complex overedge stitch therefore must be completed in the same interval in which the simpler lockstitch or chainstitch is formed. Proper sequential thread interception for either two or three thread overcasting requires accurate timing of the operation of the interacting loopers (or looper and spreader as the case may be), and as the rate of stitch formation increases, these interceptions must take place in shorter intervals and hence the timing or setting of the overedge stitching instrumentalities becomes more sensitive. Successful high speed operation depends increasingly on extreme precision in manufacture of the cooperating parts and in the initial setting up of their operating relationships to ensure proper stitch formation.

Such elements are operated generally with oscillating r reciprocating movements which involve sudden changes in velocity as direction is reversed. All such changes are accompanied by some overthrow or deflection of the moving parts in the direction of movement as the motion is arrested and then reversed. Proper design dictates that the mass of such moving parts be kept as small as practical to minimize the mass in motion. At low speeds such mass in motion does not greatly affect performance, but as the speed moves upwardly, the effect of such mass in motion becomes increasingly greater, and this unfortunately produces variable amounts of overthrow, according to the instantaneous velocity, which compounds the difiiculty in adjusting the timing of the thread interceptions so that proper stitch formation will take place at any of the intermediate speeds at which such machines are routinely operated.

Hence an important limiting factor in the satisfactory high speed operation of safety stitch machines is the difficulty experienced in obtaining proper operation of the overcasting portion of the stitchforming instrumentalities at such speeds. It is evident therefore that if the rate of operation of the overcasting elements be lowered, the difficulty will be lessened, and wear of the operating parts will be reduced and sophisticated lubrication systems will not be required.

Incidentally, decreasing the rate of operation of the overcasting elements while maintaining the same work production rate for the sewing machine as a whole, makes it possible to speed up overall operation of the entire safety stitch machine up to the safe operating limits of the join seam stitching elements. As an illustration of the commercial demand for higher speed operation, the device disclosed in Patent No. 2,973,731 operates in industry use at speeds up to 5000 stitches per minute,

while the device disclosed in pending application Serial No. 30,682 operates at speeds up to 6000 stitches per minute.

The new mode of operation disclosed herein is not only useful in safety stitch sewing machines which overcast two or more superposed ply edges together as disclosed in the mentioned Sigoda patent and application, but is much more advantageous when used in the more intricate tpye of safety stitch sewing machine disclosed in Sigoda application Serial No. 43,315, filed July 18, 1960. In the latter machine, two superposed ply edges are separated and sequentially overcast as the join seam is sewn in but one operation. Such compound seams are widely used as the inside seams of the leg portions of mens trousers.

As explained in that application, it is common practice to produce such seams in three separate operations on two different types of sewing machines, a plain overedger and a join seam machine either of the lockstitch or chainstitch type. Since satisfactory ply edge coverage can be achieved by relatively long overcast stitching, the feed stroke of the plain overedger can be lengthened to produce fewed but longer overcast stitches per inch, thus greatly increasing the production rate. However, in order to obtain a satisfactory join seam, the feed stroke of the machine producing that type of seam must be adjusted to produce more stitches to the inch. This is necessary if the desired seam strength is to be realized and undesirable gapping or grinning of the seam is to be avoided as the seam is put under tension when the garment is worn.

When a safety stitch machine is used to reduce the number of sewing operations to two by simultaneously overcasting one ply edge as it is joined to a ply edge previously overcast on a plain overedger, the feed stroke must also be shortened to product a satisfactory join seam. This curtails the production capabilities of the two operation system, and since the over-casting produced by the safety stitch machine has more stitches per inch, more thread is used than in the three operation system. The separtaely overcast edges of the finished seam also present a non-uniform appearance because of the differing number of stitches per inch covering each edge. These limitations lessen the production advantage of the two operation system over the three operation system particularly if the additional thread consumption is of importance.

In an eifort to increase the production capabilities of the two operation system by using a longer feed stroke while still producing a satisfactory join seam, a safety stitch machine disclosed in Schweda et al. Patent No. 2,973,730 utilizes a tandem two thread chainstitch seam for the join seam. This machine is operated with the overcasting matching the stitch length of the overcasting produced in the plain overedger, and this would normally produce an extremely long join stitch which would be objectionable, but by simultaneously sewing a second similar stitch closely adjoining the first chainsttich, but offset by half a stitch length, a join seam is produced which while actually two separate seams, has in effect twice as many stitches to the inch as the overcast edge. According to the patent description, this produces the desired join seam strength and resistance to gapping.

The approach disclosed in the Schweda patent points up the problem involved in obtaining higher production rates, but does not offer as simple or as satisfactory a solution as that which is hereinafter described. In order to obtain the higher production rate, a more sophisticated join seam is necessary. This involves additional mechanisms, always a potential source of trouble, and also more thread consumption in the join seam. Furthermore, the

arsesse overcasting elements still operate at the same rate as the join seam stitchforming elements.

The new mode of operation disclosed herein offers advantages in the solution of the problem over what has been available in the art heretofore. It provides less wear for the looper operating elements of the overcasting portion of the safety stitch machine, and lessens the lubrication requirements because of the reduced speed. It pro vides greater thread economy than is available with any other safety stitch machine when the longer overcasting stitch is desired. It makes both the one operation and two operation systems of inside trouser leg seam production as economical in thread consumption as the three operation system, and makes them comparable with the three operation system on seam uniformity. It also makes it possible to operate the safety stitch machine at the highest rate of which the join seam instrumentalities are capable, while simultaneously, the overcasting loopers can operate at some considerably slower rate, such as a submultiple of the machine rate. In the preferred embodiment disclosed herein this rate is one half the machine rate, and thus if the join seam is being produced at ten stitches to the inch, the overcasting will be at five stitches to the inch whether the sewing machine operates at 4000 stitches per minute or some far higher rate.

In the present embodiment, since the overedge needle is carried by the same needle bar which reciprocates the join seam needle, both needles make the same number of work penetrations, but since the operation of the overcasting elements is timed so that the overedge needle thread is intercepted only on alternate needle penetrations, only half as many, but twice as long, overedge stitches are formed. The additional needle penetrations are not objectionable because the strength of the seam is not affected thereby, nor are they visible because of their location in the seam.

In the disclosures of Sigoda Patent No. 2,973,731 and the mentioned pending applications, the new mode of operation is readily achieved by changing the operating rate of only the overedge loopers and this is done by a simple gearing change.

In safety stitch machines, proper trimming of the ply edges in advance of the overcasting is necessary for uniform stitch formation. It is therefore desirable, in order not to interfere with the proper feeding of the work, to continue to operate the edge trimming cutter at the higher rate of the join seam formation rather than at the slower rate of the overcasting. The arrangement of the gearing disclosed herein maintains this operating relationship.

The manner in which these and other features of the invention are realized will become'apparent from the following description taken in conjunction with the drawings in which:

FIG. 1 is a front elevational view of an industrial type sewing machine representative of such lockstitch machines as the Singer 400, 451 and 600 classes, which was previously converted for the production of dual seams in accordance with the disclosure of Sigoda Patent No. 2,973, 731, and for the production of two thread chainstitching for the join seam portion thereof in accordance with the disclosure of Sigoda pending application Serial No. 30,682; in which certain parts of the machine have been broken away to show the various power takeoff arrangements and from which the movable edge trimming cutter has been omitted so that the overedge looper and spreader are visible; the machine disclosed being arranged to produce a two thread overedge stitch of the Federal Specification Type 503;

FIG. 2 is a top plan view of the housing which contains the drive mechanisms for the overedge elements which in conjunction with the overedge needle produces the overcasting of the ply edge or edges; this view showing the movable trimming cutter which trims the ply edges in advance of the overcasting;

FIG. 3 is an enlarged representation of several stitches d of the two different seam types simultaneously formed in the work by a sewing machine operating in accordance with the instant disclosure, the join seam of the Federal Specification Type 4-01 having twice as many stitches to the inch as the Federal Specification Type 503 overedge seam; and

FIG. 4 is a diagrammatic representation of the relative timing cycles of the join seam needle, looper and presentor over a period representing the formation of two complete chainstitches, and of the overedge needle, underlooper and overedge spreader over the same period in which only one overedge stitch is formed.

This embodiment of the invention is shown in the form of two separate mechanisms applied to an existing sewing machine of the Singer 451K type which has been modified for the purpose. Complete descriptions of the mechanisms and the modifications of the basic sewing machine needed for the purpose of adding them, will be found in the mentioned Sigoda Patent No. 2,973,731 and in application Serial No. 30,682, and reference may be had thereto for further details.

Briefly, the sewing machine has a cloth-plate 1 from the right end of which rises the standard 2 of a hollow bracket-arm 3 which overhangs the cloth-plate and termimates in a needle-head 4. A rotating upper main shaft is journalled horizontally in the bracket-arm and a corresponding rotating lower main shaft driven therefrom is horizontally supported from the undersurface of the clothplate. The upper main shaft carries the usual crank disc and pin extending therefrom and the usual pivotal connections for reciprocating the needle-bar 5 on which an additional needle holder 6 is supported. The needle-bar 5 carries join seam needle 8 for the two thread chainstitching and the needle holder 6 carries overedge needle 9.

The lower main shaft through the usual mechanism operates the feed-bar which supports a feed-dog which in conjunction with presser foot 10 serves to advance the work to the stitchforming elements. The lower main shaft also carries a pinion 11 and a spiral gear 12. Pinion 11 mates with and drives spur gear 13 fast on shaft 14 which carries an eccentric-block 15 and stud 116 which produce the rocking of arm 18 on which the thread presentor 19 is carried.

Gear 12. through the gear train indicated rotates shaft 20 and the eccentric-block and stud carried thereby and through pinman 21 causes shaft 2 2 to rock the chainstitch looper 23 transversely to the line of feed as the thread presenter 19 is rocked forwardly and rearwardly in line with the direction of feed. The interaction of needle 8, presenter 19 and looper 23 to form two thread chainstitehing is fully detailed in the pending Sigoda applica tion Serial No. 30,682.

Supported on the cloth-plate by a mounting plate 24 is a housing 25 which contains the drive mechanisms for operating the overedge looper elements and the movable edge trimming cutter 26. Drive shaft 23 connects through double universal joint 29 and a one-to-one ratio gear train with the lower main shaft to power the operating mechanism supported in housing '25.

Within the housing, shaft 28 carries eccentric 3%) which through link 31, lever 32 and shaft 3 3 drives cutter 26 at the same rate as that of the lower main shaft and hence that at which the feed dog is operated thereby. Shaft 28 also carries spiral gear 34 which .is in mesh with and drives spiral gear 35. Gears 3'4 and 35 are proportioned with a one-to-two diametrical ratio as shown so that drive shaft 36 which operates the looper drive mechanisms rotates at half the speed of shaft 28.

Shaft 36 carries eccentrics 38 and 39 which respectively operate the underlooper db and the overedge spreader 41. Under-looper 4b is carried by shaft 42 which is rocked through the linkage consisting of short-arm 43, eccentric-arm 44 and the strap portion 415 which encircles eccentric 3S. Overedge spreader 4-1 is carried by shaft 46 which is rocked by linkage consisting of short-arm 48,

rod end bearing 49, Tablock 50 and strap 51 which encircles eccentric 39.

It is clear that any other submultiple relationship could be employed so long as the resulting rate of rotation of shaft 36 permits coordinating the operation of the loopers with the reciprocation of needle 9 so that the thread interceptions required for the formation of the overcast stitching can occur properly regardless of the number of [fabric penetrations of needle 9. It is not necessary that an overedge stitch form for each penetration of needle 9 so long as acceptable edge coverage is obtained by the selected overedge stitch to join seam stitch ratio.

As may best be appreciated from FIG. 4, as the machine operates, for each 360 degrees of needle bar reciprocation, one complete join seam two thread chainstitch seam will be formed. In this same interval, only a portion of the overedge stitching will be iormed as two reciprocations of the needle bar are required to complete each overedge stitch.

As previously mentioned, the mode of operation does not depend upon the join seam being a two thread chainstitch. Obviously if the additional mechanism required to convert the original lockstitch sewing machine for .chainstitching is omitted, the machine will form lockstitching in a two-to-one ratio with the overcasting. Likewise, regardless whether the join seam is of the lockstitch or the chainstitch type, the superposed ply edges may be jointly overcast as shown in the mentioned patent and pending application Serial No. 30,682; or as shown in pending application Serial No. 43,315, the ply edges may be separated and each ply edge overcast in sequence. While the invention may be particularly useful in safety stitch sewing machines of the latter type, it can be ap preciated that it will be useful in any form of safety stitch sewing machine inwhich it is desired to produce overcasting at a diiferent stitch rate than that of the join seaming.

While a preferred embodiment of the invention has been shown and described herein, other embodiments have been indicated. It is to be understood therefore that the foregoing description and the drawings are to be taken as being illustrative of the invention and its general principles and not as limiting the scope of the invention to the details of construction shown and described. It is intended that the invention be construed broadly within the purview of the appended claim.

What is claimed, is:

A sewing machine having a single main shaft rotating at a first rate; a single feed mechanism operated from said main shaft in a one-to-one ratio; stitchforming mechanism including a single reciprocating needle bar operated from said main shaft in a one-tonne ratio; a plurality of threaded needles carried by said needle bar; said needle bar operating at the first rate; complementary loop-taker means cooperating with one of the needle for forming join seam stitches at the first rate to unite two or more fabric plies; a housing on the sewing machine, a threaded underlooper supported by the housing and cooperating with another of said needles for overcasting the edges of the fabric plies; drive mechanism tor the nnderlooper contained in the housing; an operating connection between the drive mechanism and the main shaft to operate the un-derlooper so that it coacts with the last mentioned needle only on certain of the reciprocatio-ns of said needle bar at a second rate which is a submultiple of the first rate.

References Cited in the file of this patent UNITED STATES PATENTS 1,612,821 Huber Jan. 4, 1927 2,853,036 Enos Sept. 23, 1958 2,976,730 Schweda et a1. Mar. 7, 1961 2,973,731 Sigoda -d Mar. 7, 196 1 

